To examine the relationship between parental asthma, maternal asthma control during pregnancy, and vitamin D status on risk of asthma or recurrent wheeze in children at 3 years of age.

This was a secondary analysis of the Vitamin D Antenatal Asthma Reduction Trial, a randomized, double-blind, placebo-controlled clinical trial of vitamin D supplementation versus placebo in pregnant women to prevent recurrent wheeze and asthma in their offspring. Data consisted of 806 women and their partners and infants, with data from birth up to 3 years of age. The mother or father was required to have a physician diagnosis of asthma or atopy.

The primary outcome was the first occurrence of the infant’s asthma or recurrent wheeze in the first 3 years of life, determined by parental report. The main risk variables included (1) parental asthma status, (2) maternal asthma control, and (3) insufficient vitamin D status in cord blood. Subject characteristics were compared using a t test, χ2 test, or Fisher’s exact test, and outcomes were analyzed using the log-rank trend test, Kaplan-Meier method, and Weibull univariable regression models.

A total of 218 children had asthma and/or recurrent wheeze by 3 years. The highest risk was seen among children whose parents both had asthma, as compared with parents that did not have asthma (adjusted hazard ratio [aHR]: 2.3; 95% CI: 1.35–3.84), and had an aHR of 1.70 if only the mother had asthma (95% CI: 1.17–2.40). Children born to mothers with uncontrolled asthma had a higher risk of asthma compared with children born to mothers with controlled asthma (aHR: 1.60; 95% CI: 1.02–2.54). Cord blood vitamin D level was lower among infants with asthma and/or recurrent wheeze by the age of 3 years compared with those who did not (mean difference of 5.43 ng/mL; 95% CI: 2.20–8.60).

This study found that maternal asthma is a risk factor for early childhood asthma and wheeze. This risk was further increased if both parents had asthma or if there was a lack of maternal asthma control during pregnancy. In addition, cord blood vitamin D sufficiency at delivery reduced the risk of asthma and/or recurrent wheeze by 3 years.

This study provides additional information about the impact of paternal asthma and the mother’s asthma control on the risk of asthma and/or recurrent wheeze in offspring. Limitations include participant report of data and the potential lack of generalizability to nonatopic populations. Strengths include the large sample size and cohort study design. Maternal asthma control should be monitored during pregnancy not only for maternal health but also for the possibility of reducing the risk of asthma or recurrent wheeze in the child. Vitamin D deficiency is another potential risk factor, and there are ongoing studies in which researchers are evaluating the effects of supplemental vitamin D on development of allergic disorders.